1. Field of the Invention
The present invention relates generally to straddle packer tools for straddling and isolating a casing interval within which well treatment operations, such as production formation fracturing, are typically conducted. More particularly, the present invention concerns a straddle packer tool having spaced inflate packers for sealing within a well casing to define a sealed casing interval and having an inflate control system that is controllable from the surface for inflation of the packer elements, storing and releasing stored packer inflation pressure and for controlling differing modes of tool operation. The present invention also concerns a method, controllable from the surface, for flow responsive inflation of packer elements, storing inflation pressure within the packer elements, and selective mechanically actuated deflation of the packer elements to enable use of a straddle tool for interval treatment and to facilitate movement of the straddle packer tool to different subsurface locations and to facilitate retrieval of the tool.
2. Description of the Prior Art
The term “straddle stimulation tools”, as used herein, is intended to mean any well servicing tool having spaced packer elements and which is used within a well to isolate a particular subsurface zone or interval, typically having a casing with perforations, the tool having a fluid supply for various well treatment operations, such as acid injection, formation fracturing, with proppant injection into formation fractures that develop during fracturing, and any other well service operation where a fluid is injected into a casing interval for any character of treatment of the formation surrounding the casing interval. The term “element” as used herein is intended to mean a packer element, particularly an inflatable packer element, which is mounted on a well stimulation tool. Two or more packer elements are supported in spaced relation by a well stimulation tool and when sealed within the well casing, define a casing interval into which well stimulation fluid is pumped for treatment of a formation zone that is communicated with the well casing by perforations in the casing.
The production of an oil or gas well can often be improved by injecting treating or stimulation fluids directly into the formation(s) through perforations in the casing. Moreover, the benefits are often greater if, for a given well, multiple zones are isolated and treated separately. In order to isolate a particular zone, it must be effectively sealed off from the rest of the well. This can be done using elastomeric packer elements that seal with the well casing and block the annulus between the well casing and the downhole tool; the packer elements, when positioned in straddling position, are located above and below the casing perforations and thus straddle a given zone within the casing. Treatment fluid is then injected through a conveyance and fluid supply mechanism, such as coiled tubing, and the fluid is forced out of the tool, in between the packer elements, and into the formation via the casing perforations.
In many wells, the stimulation tool must pass through small diameter production tubing before reaching the larger diameter casing. This requires the use of inflatable sealing elements that, when deflated and thus contracted to a small dimension, will pass through production tubing and other restrictions and, after inflation, will have enough volume and mechanical integrity to fill and seal the large annulus that typically exists between the tool and the casing wall. Furthermore, the tool must be capable of directing fluid that is pumped from surface through different paths at the various stages of the tool operation. For example, at certain times the fluid must be directed into the packer elements for packer inflation, above the upper sealing element, and in between the elements for formation treatment.
Inflatable straddle stimulation tools in the market today require varying degrees of coiled tubing manipulation in order to accomplish packer deflation and to shift the tool from one position to another within the well casing and to direct the fluid pumped from surface. The inherent difficulties in accomplishing these features, particularly in deep or deviated wells, result in straddle tools that are often unreliable and difficult to operate.